The present invention is in the field of oil and/or gas well casing perforation apparatus, procedures and methods. More specifically, the present invention is directed to a unique apparatus and method employing a high pressure fluid driven punch for cutting an opening in a well casing and subsequently cutting a passageway through the surrounding earth by the use of a high pressure jet for a substantial distance outwardly beyond the casing for permitting the flow of liquid or gaseous hydrocarbons into the casing.
The vast majority of oil and gas wells are drilled by the use of rotary drilling procedures in which drilling mud containing extremely fine particles is forced downwardly through the drilling string and out through the bit for the removal of cuttings, cooling and other beneficial results. A commonly employed material in drilling mud comprises extremely small particles of barite. It has been found that the earth surrounding a drill bore is contaminated outwardly by the drilling fluid for a distance of a meter or more beyond the bore. This contamination, being largely formed of minute particles from the mud, frequently presents a substantial barrier to the inflow of hydrocarbons to the well casing.
Moreover, invasion of the formation by cementing and well completion fluids creates additional formation contamination. The zone around a well bore which has been contaminated or plugged by drilling fluid, cement or completion fluids is termed the invaded zone or damaged zone and the effect is called formation damage, skin damage or skin effect. "Skin effect" is a petroleum engineering measure of the extent of damage or resistance to flow of fluids around a well bore and is expressed as a dimensionless number. A high skin effect number or factor representing extensive formation damage for example would be 10, whereas a low skin effect number would be 0.
A number of expedients have been proposed and employed in an effort to provide flow passageways through the surrounding strata or to remove skin effect for permitting and increasing the flow of hydrocarbons into the well casing. Probably the most common expedient is the use of projectiles fired from gun-like devices positioned in the casing; however, the projectiles from such devices are normally incapable of penetrating beyond the zone of contamination and optimum flow conditions consequently cannot normally be achieved by the use of such devices. Consequently, a variety of other proposals for penetrating the surrounding strata have come forward. For example, U.S. Pat. No. 4,022,279 proposed a method of boring spiral bores a substantial distance outwardly from a well casing for increasing production. However, this patent does not disclose a specific apparatus for effecting the desired spiral bores and it is not certain that such structure actually exists.
U.S. Pat. No. 3,370,887 discloses a fracturing device employing a blow-out plug 11 which is blown radially outwardly through the well casing by high pressure injected into the housing in which the plug is mounted. U.S. Pat. Nos. 3,400,980 and 3,402,965 (both to Dahms et al.) both disclose a tool which is moved downwardly out the lower end of the well casing and from which extendible pipe or hose members more outwardly while discharging high pressure liquid to provide a cavity at the lower end of the well. U.S. Pat. No. 3,402,967 (Edmunds et al.) discloses a device that is similar in operation to the Dahms et al patents.
U.S. Pat. No. 3,547,191 (Malott) discloses an apparatus that is lowered into a well for the discharge of high pressure liquid through nozzle means 26, 27. The discharge from the nozzle means passes through previously formed openings 35 in the casing.
U.S. Pat. No. 3,318,395 (Messmer) discloses a tool including a body of solid rocket propellant fuel 34 which is lowered to a desired position in a well. The rocket fuel is ignited and the exhaust discharges outwardly through nozzle means 36 to cut through the casing and the cement surrounding the casing. The discharge from the rocket includes abrasive particles which aid in the cutting operation and also serve to cut as notch in the surrounding formation to fracture same and hopefully improve production. However, as the discharge from the rocket, or any other fixedly positioned jet means, erodes the formation, the standoff distance between the nozzle and the formation increases and the effectiveness of the apparatus is greatly reduced.
U.S. Pat. No. 4,050,529 (Tagirov et al.) discloses a tool which is lowered down a well casing and includes nozzle means through which high pressure abrasive containing water is pumped to cut through both the casing and the surrounding formation. The use of abrasive materials pollutes the well forever in that it creates monumental wear problems in valves, pumps and the like subsequently used with the well. Moreover, the abrasive is absorbed in the surrounding formation and also blocks the pores of the formation.
U.S. Pat. No. 4,346,761 (Skinner et al.) discloses a system including nozzles 20 mounted for vertical up and down movement in the casing to cut slots through the casing. The nozzle means does not protrude beyond the casing. However, the high pressure jet discharged from the nozzle would apparently effect some cutting of the surrounding strata.
Other patents disclosing high pressure nozzles for cutting well casing include U.S. Pat. No. 3,130,786 (Brown et al.); U.S. Pat. No. 3,145,776 (Pitman) and U.S. Pat. No. 4,134,453 (Love et al.). U.S. Reissue Pat. Re. No. 29,021 (Archibald) discloses an underground mining system employing a radial jet which remains in the well before for cutting the surrounding formation. U.S. Pat. No. 4,317,492 (Summers) discloses a high pressure water jet-type well system usable in mining and drilling operations in which a nozzle providing a jet is moved out the bottom of the well and is then moved radially. U.S. Pat. No. 3,873,156 (Jacoby) also discloses a jet-type mining device movable out the lower end of a well for forming a cavity in a salt well. U.S. Pat. No. 4,365,676 (Boyadjieff) discloses a mechanical drilling apparatus moveable radially from a well for effecting a lateral bore hold. A number of additional U.S. patents disclose the employment of high pressure nozzle means for cutting the strata adjacent or at the bottom of a well with these patents including U.S. Pat. Nos. 2,018,285; 2,258,001; 2,271,005; 2,345,816; 2,707,616; 2,758,653; 2,796,129 and 2,838,117.
None of the aforementioned prior art devices have achieved any substantial degree of success due to a variety of shortcomings. For example, those devices which simply project a high pressure jet from a nozzle positioned inside the casing cannot cut outwardly from the casing a sufficient distance to be truly effective. Moreover, the direction and extent of the cut provided by such devices is subject to a number of variable parameters including the nature of the surrounding formation and it is therefore difficult to achieve a predictable result. One problem with all high pressure-type jet devices operating through the wall of the well casing is that an aperture must be cut in the casing and the surrounding cement as a prerequisite to cutting through the surrounding formation. In some of the prior known devices the aperture can be cut with the nozzle jet itself whereas other devices require the use of separate mechanical cutting means. Those devices using nozzle jets for cutting the casing suffer from a very serious drawback in that the cutting liquid frequently includes abrasive particles which remain in the casing and can subsequently adversely effect valves or other components such as pumps or the like into which some of the abrasive components are eventually indicated.
The use of separate mechanical cutting devices suffers from the shortcoming of requiring substantial additional expense both in terms of the cost of the extra equipment and the cost of time required in using same for cutting the casing. This is true because such use will normally require lowering of the cutting device to the bottom of the well, cutting of the casing and subsequent removal of the cutting device and positioning of the jet means in the casing prior to usage of the nozzle jet-type cutter. The positioning and removal of tools from the well normally requires a time consuming and expensive pulling and replacement of the string.
A common shortcoming of all types of penetrators prior to the invention of U.S. Pat. No. 4,640,362 (Schellstede) was that they simply did not result in adequate penetration of the formation outwardly of the casing a sufficient distance to achieve improved production. Therefore, there had been a very substantial need for apparatus capable of effectively penetrating the earth formation surrounding a well casing for a distance outwardly beyond the casing outside the contamination zone surrounding the casing. A particular problem was the inability of many devices prior to Schellstede to maintain a proper standoff distance from a cutting jet providing means.
The invention of the aforementioned Schellstede patent represented a very significant advance in the penetration art in that it permitted penetration of the earth formation well beyond the contamination zones surrounding the casing as to provide a very superior performance compared to the prior known devices. Additionally, it permitted an initial jetting of cement away from the casing prior to outward movement of the jet providing semi-rigid, extendable, conduit and nozzle extension device. Moreover, the Schellstede device had other advantageous features flowing from its unique design. However, the device of the Schellstede patent is somewhat complicated in requiring hydraulic circuitry which includes two nitrogen accumulators, rotor actuators and valve sets and tubing flow lines all of which were mounted in a ten foot housing. Additionally, operation of the Schellstede device requires that pressurized working fluid be provided to the apparatus at four different pressures each at different times during each cycle of operation. The overall length of the complete apparatus is consequently substantial and the use of the flow lines creates a substantial potential for leakage in view of the high pressure required during usage of the apparatus.
Prior U.S. Pat. No. 4,790,384 represented an improvement over the device of the aforementioned U.S. Pat. No. 4,640,362 in that it used only a single accumulator and was less complicated and more trouble free. However, the invention of the aforementioned application still included complexities such as those resultant from the use of the single accumulator in the control head which rendered the apparatus somewhat time consuming to calibrate and use for some applications. Also, the device of the prior application required the expensive boring of lengthy bores through solid steel as part of the construction of the control portion of the apparatus.
It is consequently the primary object of the present invention to provide a new and improved apparatus for penetrating earth formations around a well casing which is less complicated, easier to use, less expensive to machine and more trouble free than the prior known well penetration devices.
Another object of the invention is the provision of a simplified control head for a lance-type well penetrator.